Signaling system



April 14, 1942' D TT 2,279,978

SIGNALING SYSTEM Filed Odt. 25, 1940 A TTORNE V Patented Apr. 14, 1942 SIGNALING SYSTEM Danforth K. Gannett, Mountain Lakes, N.

assignor t-o Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 25, 1940, Serial No. 362,782

9 Ciaims.

This invention relates to signaling systems and particularly to systems employing voice frequenc currents for transmitting signals.

Objects of the invention are an increase in the reliability of alternating current signaling and the prevention of false operation in response to interference currents.

In signaling systems in which current of one or more voice frequencies is used for signaling, the signal receiver must respond to signaling current without being responsive to voice currents or interference currents of signaling frequency. It is known in such systems to employ frequency selective or time delay arrangements for preventing false signal operations.

According to this invention, false signal operation is prevented in an alternating current signaling system by distinguishing between signaling currents which are of sine wave form and other currents due to the fact that a sine wave is the only wave form the mathematical derivative and integral of which are exactly alike. Representing the signal wave by E sin oi, the first derivative is Ew cos wt and the integral is cos wt By applying the signal wave to differentiating and integrating channels, the outputs if adjusted to be equal in magnitude will cancel each other when combined. For any other wave, however, the derivative and integral will be different and the sum of the output of the two channels will not be zero. Therefore, the differentiating and integrating channels in combination may be used as a guard channel to prevent a signal respons to any other than a sine wave.

. A feature of the invention is a signal receiver for connection to a line through which voice currents and signals consisting of voice frequency currents are transmitted, operation of the signal relay being effected by the energization of one of its windings responsive to the transmission of signal current through the line, the operation of the relay while voice currents are being transmitted through the line being prevented by the energization of another winding connected to the combined output of an integrating channel and a differentiating channel.

A signal receiver arranged in accordance with the invention is shown in the drawing which consists of a single figure, The invention is not limited, however, in its application to the specific arrangement shown but may be applied generally to any device which it is desired to make responsive to sinusoidal waves and unresponsive to waves of other shape.

Referring to the drawing, a signal receiver SR is connected to a line L over which signals and voice currents ar transmitted. The receiver SR comprises transformers Ti, T2 and T3, amplitiers 2! and 22, detectors 3| and 32 and a polarized signal relay Three batteries are shown, a battery 3! for energizing the cathodes of the amplifier and detector tubes, a battery B2 in the anode-cathode circuits of these tubes, and a battery B3 for biasing the grids of the detector tubes, Voice curents and signal currents in line L are applied through windings ii H and i2 of transformer T2 to amplifiers 2i and 22 in parallel and through windings 25 and 2'! of transformer to the detector 32. The outputs of am ers iii are differentiall combined b windings and applied through wir a of -sformer T2 to the detector rh transformer T3 and detector coi itute a signal channel for operatively energizing the lower winding of relay 3t; and the transformer Ti, detectors 2i and 22, transformer T12 and detector 3! constitute a guard channel for energizing the upper winding of relay to prevent its response to voice currents response while voice currents are being trans mitted over line L. The guard channel effect is obtained by connecting transformer windings H and I2 to the amplifiers 2! and 22 in such a manner that the output of amplifier H is proportional to the derivative of the line voltage across winding it of transformer Tl and the output of amplifier 22 is proportional to th integral of the line voltage. It is known that the current through a capacity is the derivative of the potential across it, and that the potential across a capacit is the integral of the current through it. Accordingly, the winding ll oftransformer Tl is connected through a condenser l3 to the grid of tube 2i; and a resistor it, having a very small impedance at the signaling frequency as compared with that of condenser I3, is connected in series with condenser i3 and winding ll so that the current through resistor 55, and therefore the potential impressed on the grid of tube 2i, are substantially the derivative of the voltage across winding ll. And the winding 52 of transformer Ti is connected through a resistor it to the grid of tube 22; and a condenser Hi, having a reactance which is very small at the signaling frequency compared to the im eda-nce of the resistor i4, is connected in series with winding l2 and resistor M, so that the voltage across the condenser, and therefore the potential impressed on the grid of tube are substantiall proportional to the integral of the voltage across winding l2.

Representing the voltage applied by signaling current by E sin wt, the first derivative is Ew cos wt and the integral is E cos wt If then the outputs of detectors 2| and 22 are Sln(wt+a) is suddenly applied to a capacity C adjusted to be equal in magnitude and are difand a resistanceR in series. Then ferentially combined, the resultant will be zero; E

there W111 be no current m the l l where e is the potential across the condenser. cult of detector 3!, so that the energlzation of v From this the lower winding of relay in the output cir- ,7 E Sin(wt+a) e cuit of detector 32 will cause the operation of i=- relay 30. The operation of relay 3U closes a but circuit through conductors 33 and 34 for effectv d (1 ing any desired result. In response to the ap- 13 q: C6 and i= =C- plication of a voltage of any wave form other than that of a sine Wave, the derivative and integral will be unlike in form and consequently the output of amplifier 2| will not be canceled by the output of amplifier 22; and the resultant energization of the winding 25 of transformer T3 dy effects a current in the output circuit of dei- ZI=Q tector 3| which energizes the upper winding of relay 3!! to prevent the operation of the relay by Whose solunon may be Shown to be energization of its lower winding by current in ii) z Lf f the output circuit of detector 32. By comparison Since the processes of integration and diifert t entiation are somewhat imperfect due to the z E finite ratio of the shunt to series impedances, a e itz GI Sm winding 28 of transformer T3 adds a small part :3 Integrating Equating these values of 2' and rearranging de e, E

Sln(wi+oz) (1) This may be compared with of the energy from the signal channel to the Wh 5:0, :0 Therefore input to tube 3| to correct for secondary efiects 7 2 as hereinafter explained. E cos sin 1 If the relative sensitivities of the amplifiers a a and detectors are properly chosen, relay 3!] will Substituting in (2) 1R-Es1n (wt-Fa) e E[ sin (wt-ta) +w+w2 cos (wt+a) +6 (m Slll a;,; i; cos 01)] (4) be operated in response to signal currents alone Equations 3 and 4 may be taken to represent but will be prevented from operating when voice the potentials at the outputs of the integrating or other non-sinusoidal currents are being transand differentiating networks in Fig. 3. Let the mitted in line L. The performance of the arsteady-state potentials in the output of each rangement, both to steady-state and to transient ir uit t th signaling frequency /2,, conditions occurring at the start of a signal will bear a ratio of A t t applied potential be analyzed to S w that the arrangemfimt W111 sumed to be the same for both circuits) Then in provide the satisfactory operating margins. It i Equation 3 all-Awe and in Equation 4 w1=wo/A is shown that the translent at the start of a Also let w Sw0. Substituting these values in (3) signal is of the nature of two superposed conand (4) and adding the two equations we t denser discharge curves, one large but of short ge duration and the other small but of longer duration. The transient contains no oscillations of er+iR 2 S2 the signal or any other frequency. E S2 1 sin (wt+ oz) If a signal, E sin wt, is applied to a difieren- A2 tiating network, the resultant is proportional to S Em cos wt; and if it is applied to an integrating 3 AS network, the resultant is proportional to S2 cos (+00 These cosine waves are opposite in phase so that cos Sin if they are multiplied by suitable constants to SZ+A2 make them equal, and are then added, the result u t 1 S will be complete cancelation or zero. This is true for the steady-state condition, but the signal Sm A cos a must begin and end, and it is of interest to in- 2 l h i vestigate the nature of the starting and stopping transients. c

Assume th t t ti tzo, a potential E Since A 1s small compared with unity, this equation may be simplified by omitting the higher order infinitesimals.

From this, the relative sensitivity of the guard and signal channels is determined. For example, if it is desired that the circuit respond in a time =m(s )sn w+a A(-s cos wt+a 1 A A t A 5 t=A QO,

'0 +3 35111 the signal channel must have a sensitivity of m about .37A. The steady-state sensitivity of the guard channel is then the same as that of the '5 (S111 005 10 signal channel at a frequency determined by the 1 It will be noted that when 8:1, the only term re anon 1 left after a time long enough for the exponential ,g 2 7 terms to disappear is the first. It is this term S which is compensated for by introducing in oppo- 2 r 80 site phase through winding 28 a small amount w o (2A of the original signal in the input to the At frequencies farther from the signal frequency guard channel detector 3|. With this compensathe guard channel sensitivity exceeds that of tion, the sinusoidal components applied to the the signal channel, and at frequencies closer to detector become the signal frequency the guard channel is less 1 2 1 sensitive than the signal channel. A Sg) sin(wi+oz)+A S' )COS(wi+ a) (7) From the above, it is apparent that satisfactory operating margins are obtained in the signal and both disappear at the s1gnaling frequencies receiver SR 1 In the neighborhood of the slgnalmg The specific arrangement described above to quency, the first term is small compared to the illustrate the invention may be altered in detail second and ay be neglected- Without departing from the spirit of the in- The magnitude of the transient terms vention. For example, amplifiers 2| and 22 may third and fourth terms) of Equation evidently in practice be any form of amplifier utilizing d p d upon the of the 5131131 Wave other types of tubes than triodes and consis at the time t =0; Also, 1t w1ll be noted that the mg f more than one Stage of amplification; 3| second translent ternr IS in general the largest, and 32 may be any form of detector; and any but has a veryshPrt F constant, suitable responsive device may be used in place ing use of approximations in which higher order of the relay 30 and conductors 33 and infinitesimals are neglected, the sum of the What is claimed is: transient terms is given in the following table 35 1. In a signaling system including a line for avarlety of condmons assummg jected to voice currents and to signals consist- Sum of transient terms ing of voice frequency currents of sine wave form,

A 1 1 l or Formula i=0 i= ttt 2% E A o 1 A2 A e' A2+ e W l L J K i A2 A (%g e (1-A2) 1 6H1 6 e e E 1A A T T /T T /T T -Awt -1 (1-A) l-A 1 -An I J2 (As +6 \/2 V26 2A 2A( )6 Ae AS A Awqt(1--A A A A(1A) A51 Ae A 0 A(e"' -e O A(1e" A Ae Ae As noted above, the time constant of the second transient term is very short so that for values of if greater than 1 /w[! (the time corresponding to one radian of the signal wave) it disappears in comparison with the first transient, (except when Aw0t 1 A At t= (one radian), the transient is 3 1 1 p t= radians the transient L, .37 S

t= i cycles the transient is .002 S a signal receiver for responding to incoming signals, said receiver comprising a difierential signal relay, a signal channel for effecting the operative energization of a first winding of the relay responsive to signaling currents, and a guard channel consisting of two amplifiers in multiple and a detector controlling the energization of a second winding of said relay, the output circuits of said amplifiers being ifferentially connected to the input circuit of said detector, the input circuit of one of said amplifiers being arranged so that the current in its output circuit is proportional to the derivative of the current in the line and the input circuit of the other amplifier being arranged so that the current in its output circuit is proportional to the integral of the current in the line, the currents in the output circuits of said amplifiers being equal in response to signaling cur-rents whereby the secnd winding of said relay is ineffective to prevent the operation of said relay upon energization of its first winding, the current in the output circuit of said other amplifier in response to voice currents being larger than the output of said one amplifier to effect the energization of the second Winding of the relay and thus prevent the operation of the relay.

2. In a signal device for connecting with a line through which voice currents and voice frequency signaling currents of sine wave form are transmitted, a polarized signal relay, a signal channel for energizing an operating Winding of said relay responsive to current in a connected line, and a guard channel for energizing a biasing winding of said relay responsive to voice currents, said guard channel comprising two amplifiers, means differentially applying the outputs of said amplifiers to said biasing winding, and means controlling the level of energy applied to said amplifiers responsive to currents in said line so that the current in the output circuit of one of the amplifiers is proportional to the derivative of the current in the line and the current in the output circuit of the other amplifier is proportional to the integral of the current in the line, the current in the operating winding of said relay responsive to signaling current effecting the operation of the relay and the current in the biasing winding of the relay preventing the operation of said relay responsive to voice currents.

3. In a signal device for connection with a line through which voice currents and voice frequency signaling currents of sine Wave form are transmitted, a polarized signal relay, a signal channel for energizing an operating winding of said relay responsive to current in a connected line, and a guard channel for energizing a biasing winding of said relay responsive to Voice currents in a connected line, said guard channel comprising two amplifiers, means differentially applying the outputs of said amplifiers to said biasing winding, and means controlling the level of energy applied to said amplifiers responsive to currents in said line so that the current in the output circuit of one of the amplifiers is proportional to the derivative of the current in the line and the current in the output circuit of the other amplifier is proportional to the integral of the current in the line, the current in the operating winding of said relay responsive to signaling current effecting the operation of the relay and the current in the biasing winding of the relay preventing the operation of said relay responsive to Voice currents and preventing the operation of said relay responsive to currents having a voice current component.

4. In a signal device, a signal relay, means comprising an input transformer for energizing an operating winding of said relay, another input transformer, a first amplifier, a second amplifier, means connecting said first amplifier to said other input transformer so that the current in the output circuit of said first amplifier is proportional to the derivative of the energy applied to said other input transformer, means connecting said second amplifier to said other input transformer so that the current in the output circuit of said second amplifier is proportional to the integral of the energy applied to said other input transformer, and means differentially combining and applying the outputs of said amplifiers to energize another winding of said relay to oppose the operation of the relay, the outputs of said amplifiers being equal and opposite responsive to sine wave signaling current applied to said input transformers, the energization of said operating winding being sufiicient to operate the relay responsive signaling current alone, said other winding being operatively energized by the combined outputs of said amplifiers to prevent the operation of said relay when voice currents are applied to said input transformers.

5. In a signal device, a signal relay, means comprising an input transformer for energizing an operating winding of said relay, another input transformer, a first amplifier, a second amplifier, means connecting said first amplifier to said other input transformer so that the current in the output circuit of said first amplifier is proportional to the derivative of the energy applied to said other input transformer, means connecting said second amplifier to said other input transformer so that the current in the output circuit of said second amplifier is proportional to the integral of the energy applied to said other input transformer, and means differentially combining and applying the outputs of said amplifiers to energize another winding of said relay to oppose the operation of the relay, the outputs of said amplifiers being equal and opposite responsive to sine wave signaling current applied to said input transformers, the energization of said operating winding being sulficient to operate the relay responsive to signaling current alone, said other winding being operatively energized by the combined outputs of said amplifiers to prevent the operation of said relay when voice currents alone are applied to said input transformers and also when both voice and signaling currents are simultaneously applied to said input transformers.

6. A signal device comprising a polarized signal relay, an input transformer and a detector constituting a signal channel for energizing an operating winding of said relay, a second input transformer, the primary windings of said input transformers connected in parallel, a first amplifier, a second amplifier means comprising a secondary Winding of said second transformer and a condenser and a resistor connected in series With said winding for impressing on the grid of the first amplifier a potential proportional to the derivative of the level of energization of the primary winding of the second transformer, means comprising another secondary winding of said second transformer and a condenser and a resistor in series with said other secondary Winding for impressing on the grid of the second amplifier a potential proportional to the integral of the level of energization of the primary winding of the second transformer, means comprising a third transformer differentially combining the outputs of said amplifiers, and means comprising a detector applying the combined outputs of said amplifiers to a biasing winding of said relay.

'7. A signal device comprising a polarized signal relay, an input transformer and a detector constituting a signal channel for energizing an operating winding of said relay, a second input transformer, the primary windings of said input transformers connected in parallel, a first amplifier, a second amplifier means comprising a secondary Winding of said second transformer and a condenser and a resistor connected in series with said winding for impressing on the grid of the first amplifier a potential proportional to the derivative of the level of energization of the primary winding of the second transformer, means comprising another secondary winding of said second transformer and a condenser and a resistor in series with said other secondary winding for impressing on the grid of the second amplifier a potential proportional to the integral of the level of energization of the primary winding of the second transformer, means comprising a third transformer differentially combining the outputs of said amplifiers, and means comprising a detector applying the combined outputs of said amplifiers to a biasing winding of said relay, the outputs of said amplifiers being equal and opposite responsive to sine wave signaling current applied to said input transformers and the energization of the operating winding of the relay being efiective to operate the relay responsive to signaling current, the outputs of said amplifiers being unequally responsive to voice currents and the biasing winding of the relay being thereby energized sufiiciently responsive to voice currents to prevent the operation of the relay when voice currents are applied to said transformers.

8. A signal device comprising a polarized signal relay, an input transformer and a detector constituting a signal channel for energizing an operating winding of said relay, a second input transformer, the primary windings of said input transformers connected in parallel, a first am plifier, a second amplifier means comprising a secondary winding of said second transformer and a condenser and a resistor connected in series with said winding for impressing on the grid of the first amplifier a potential proportional to the derivative of the level of energization of the primary winding of the second transformer, means comprising another secondary winding of said second transformer and a condenser and a resistor in series with said other secondary winding for impressing on the grid of the sec ond amplifier a potential proportional to the integral oi the level of energization of the primary winding of the second transformer, means comprising a third transformer differentially combining the outputs of said amplifiers, and means comprising a detector applying the combined outputs of said amplifiers to a biasing winding of said relay, the outputs of said amplifiers being equal and opposite responsive to sine wave signaling current applied to said input transformers and the energization of the operating winding of the relay being effective to operate the relay responsive to signaling current, the outputs of said amplifiers being unequally responsive to voice currents and the biasing winding of the relay being thereby energized sufficiently responsive to voice currents to prevent the operation of the relay when voice currents are applied to said transformers alone or in combination with signaling current.

9. In a signaling system, the method of selectively distinguishing between alternating signaling current of a sine wave form and current of other wave form, said method comprising rectification of the received alternating current for efiecting a signal operation responsive to sine Wave current, amplification of the received alternating current to obtain a current which is pro-- portional to the derivative of the amplitude of the received current, amplification of the received alternating current to obtain a current Which is proportional to the integral of the amplitude of the received current, and the difierential combination of the tWo amplified currents for preventing a signal response to received a1- ternating current of other than sine wave form.

DANFORTH K. GANNETT. 

